1. Field of the Invention
The present invention relates to a radiotherapeutic system and a radiotherapeutic dose distribution measuring method, in radiation treatment performed by emitting radiation from the outside of the body of a patient to an affected region (treatment for applying X-rays from the outside of the body of a patient to an affected region), capable of preventing excessive irradiation to an affected area and a normal tissue by measuring an actually irradiated region in the patient and actual dose and providing the result in a predetermined form.
2. Description of the Related Art
In radiation treatment typified by external X-ray radiation therapy, before the treatment, an irradiation plan (the direction and the dose of radiation to an affected region) is made on a patient image. On the basis of the irradiation plan, irradiation to the patient is performed. However, at present, there is no means for confirming whether irradiation is actually performed to the patient with the planned position and dose or not. Even if insufficient irradiation to an affected region or excessive irradiation to a normal tissue occurs, it is not noticed. In some cases, using a phantom and an X-ray detector prior to irradiation, whether planned irradiation can be performed or not is confirmed. However, it is difficult to place a patient in a position according to the irradiation plan, on a bed different from a phantom which is easily portable and whose position can be freely adjusted. The confirmation prior to radiation does not completely assure the planned irradiation to the patient.
A technique of acquiring a cross-sectional image by using scattering radiation is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-146426. According to the technique, scattered X-rays in an X-ray subject are detected to obtain a cross-sectional image of the subject. The characteristic of the technique is that a scan is performed with a pencil beam and a three-dimensional scattering radiation image of the subject is reconstructed. That is, the technique assumes only the pencil beam but is not directed to obtain a scattering radiation image of a region through which a beam having a limited width passes (a spatial distribution of dose of a therapeutic beam), which is used in X-ray treatment. Since forward scattering is dominant in the scattering in a subject of a therapeutic beam (a few MeV) having high energy, when a detector is disposed in the incident X-ray direction, it is difficult to distinguish scattering radiation and penetrating radiation from each other. A correcting process is therefore necessary for detection of scattering radiation.
Amid mounting social concern over medical errors, also in radiation treatment, excessive irradiation to a patient was reported and it became an issue. It is predicted that recording of the “fact” of medial acts performed such as a region in a patient and a dose of irradiation is becoming important more and more. In the field of external X-ray radiation therapy, attempts to irradiate an affected region more precisely are being made such as a method of irradiation so as to synchronize and trace motion of a tumor in a patient caused by breathing or the like, a method of collimating a therapeutic X-ray beam in accordance with the shape of a tumor and irradiating the tumor with the beam, and the like. The object of the precise irradiations is to concentrate the dose to an affected region. Therefore, if the therapeutic X-ray beam is off from the irradiation target, normal tissue is considerably damaged. As the irradiation is becoming more precise, it is becoming more important to check if the irradiation is performed as planned.